Ultraviolet (UV) lamp systems may be either microwave power UV lamp systems or medium pressure mercury vapor “ARC” lamp systems. UV lamp systems are used in high speed manufacturing processes to cure inks, coatings, photoresists, and adhesives in a variety of applications. These applications may include, for instance, decorating, laminating, hard-coat protection, circuit board conformal coatings, photoresist, photolithography, photostabilization, printing, and solar simulation. These systems have a wide range of uses and can be used, for example, in the curing of polymers such as photo polymer paints, the curing of inks and coatings, photo activation of adhesives, production of compact discs, and in photo resistant activation. A UV lamp produces high intensity radiation energy in the UV, visible, and infrared spectrums. This high intensity radiation energy may be used to cure inks, coatings, photoresists, and adhesives that are applied to a variety of substrates, such as paper, plastic film, wood, and metal.
The typical UV lamp system includes an irradiator to produce high intensity UV light, a power supply to provide electrical power to the irradiator, and an inter-connecting high voltage cable. The microwave powered UV lamp system has an irradiator that is equipped with one or more magnetrons. The magnetrons convert the electrical power received from the power supply to radio frequency (RF) energy in a range of generally from approximately 2445-2470 MHz. The microwave energy produced by the magnetrons in the irradiator is guided into a cavity which is encapsulated by an RF screen. An electrodeless medium pressure mercury-vapor lamp (or bulb) is positioned inside of this cavity. For UV curing applications, the bulb is typically formed in the shape of a tube with a slight “hour-glass” shape, and is constructed of quartz. For imaging and semi-conductor applications the bulb is typically spherical. The bulb may be filled with mercury, argon, and/or metal halides such as iron and gallium. The fill inside of the bulbs may absorb the microwave (RF) energy and, consequently, change to a plasma state. The plasma produces radiation energy in the UV lamp system which is in the form of UV, visible, and infrared energy.
The microwave powered UV lamp system is provided with an RF screen in order to capture and seal the RF energy within the cavity where the electrodeless bulb is positioned in the irradiator. The RF screen acts as a “faraday cage” as the openings in the screen are constructed to be smaller than the RF radiation wavelength preventing the RF energy from escaping (while simultaneously energizing the fill inside of the bulbs) and permitting light energy to be transmitted through the screen openings. For instance, a conventional RF screen assembly 10 is shown in FIGS. 1 and 2. The RF screen assembly 10 is composed of a metal frame 18 with a fine mesh screen 11 of individual square or rectangular openings 12 retained therein. As can be seen in FIG. 2, a metallic wire-woven mesh gasket 14 may be employed in order to provide a seal between a main reflector and end reflectors of the UV lamp system, and between the main reflector of the UV lamp system and the metal frame 18 of the RF screen assembly 10. The gasket 14 is compressed between the metal frame 18 and a reflector when the RF screen assembly 10 is attached.
During construction of conventional RF screen assemblies, a metal strip 15, such as stainless steel, is generally welded along each of the edges of the screen 11 to hold it securely in the metal frame 18 around the perimeter. However, formation of RF screen assemblies 10 with conventional RF screens 11 create undesirable manufacturing difficulties as the screens 11 are wavy and very flexible in nature resulting from the screen 11 being formed from woven individual metal wires of small diameter. Due to the fine mesh of conventional RF screens 11, manufacturers find it difficult to align the mesh screen 11 properly in the metal frame 18, fix the metal strips 15 properly over the edge of the screen 11 in order to prepare for welding, maintain the integrity of the screen 11 during the fixturing and welding of the assembly, and maintain proper alignment and proper tension of the screen 11 in the frame 18 during the welding process.
As noted above, the RF screen 11 prevents RF energy from escaping into the surrounding environment, and subsequently allows the bulb of the UV lamp system to light. A defective RF screen 11, such as one with a hole or other defect, allows RF energy to escape and prevent the bulb of the UV lamp system from lighting, or causes a reduced output in the bulb of the UV lamp system. Additionally, an improperly installed RF screen assembly 10 will cause arcing, and thus damage to components inside of the irradiator. Further, an RF screen assembly 10 with deformed or worn gaskets 14 will also cause arcing and damage to the irradiator.
Because the diameter of the wires making up the woven mesh is so small, the conventional RF screen mesh is delicate and susceptible to damage during the operation of the UV lamp or during maintenance of the UV lamp (such as removing or re-attaching the RF screen). Additionally, during operation of the UV lamp, the screen may be exposed to parts that can pass under the lamp and come in contact with the screen and potentially causing irreparable damage to the screen (such as creating tears and holes in the screen). If the individual wires are broken, the short lengths of wires may act as antennas in the RF field. The broken wire receives RF energy at such power to melt and erode away the end of the wire. If the screen is contaminated such that good electrical conductivity is not available between the broken wire and the crossing wires, the erosion process can continue until the wire erodes to the edge of the screen assembly 10.
The present invention improves upon current microwave UV lamp systems by providing for an improved RF screen and RF screen assembly that achieves improved light output.